A one-open end tilting rotary furnace is used in the metal industry to melt dirty metal (see for example U.S. Pat. No. 6,572,675 in the name of Yerushalmi, U.S. Pat. No. 6,676,888 in the name of Mansell) such as aluminium, from scrap that contains impurities, including organic material. Mare specifically, these furnace are used for aluminium dross processing. Typically these furnaces operate at a high temperature, for example in the range of 1400° F. to 2000° F. generally, after processing the metal scrap is in a molten state (fluid condition). These furnaces use either air fuel burners or oxy-fuel burners to heat and melt the metal scrap in the furnace. Typically these furnaces use burners that operate with an oxygen to fuel ratio in the range of 1.8 to 1.21 as stated in U.S. Pat. No. 6,572,675 (Yerushalmi). This range ensures that almost full oxidation takes place of the fuel injected in the furnace inner atmosphere. This high oxygen/fuel ratio ensures the high fuel efficiency (BTU of fuel used per Lb of aluminium melted) in these tilting rotary furnaces.
Furthermore, with all of these types of furnaces the exhaust gas is collected in an open hood system as presented in U.S. Pat. No. 5,572,675 (Yerushalmi) and U.S. Pat. No. 6,676,888 (Mansell). The open hood system is designed to engulf and collect the exhaust gases exhausted from the rotary furnace. The open hood system collects along with the hot exhaust gases a wide range of impurities (unburned organics, particulates, and other impurities). These impurities are entrained in the hot gases and carried with it. The open hood system also entrains, in addition to the hot exhaust gases, a considerable amount of ambient air (from outside the furnace) into the hood, leading to a full mixture of the air and the polluted exhaust gases.
US patent application no. 2005/0077658 in the name of Zdolshek discusses an open hood system that receives the polluted gases, along with the entrained air and passes it through a fume treatment system where the particulates are largely removed by a cyclone and the hydrocarbons are incinerated in a separate standalone incinerator. The gases exiting the incinerator are exhausted toward a baghouse. This arrangement is designed so as to treat the gases prior to exhausting it.
An example of using the exhausted gases to recover some heat from the flue is disclosed in U.S. Pat. No. 4,697,792 in the name of Fink. In this patent the hot gases travel inside a recuperator which uses these gases to preheat the combustion air which is then blown through a blower into the burner. Hence, it is an open circuit system, with exhaust gases used only for preheating the combustion air.
Typically in these furnaces, at the end of the melting cycle, the furnaces tilt forward, and empty the molten metal first into metal skull containers. Then the residue which could be a combination of iron, and other residual impurities including salts used in the process, and aluminium oxides, are skimmed from the furnace internals through protruded skimming devices.
The advantages of the tilting rotary furnace (a single operational entry point furnace) mentioned in U.S. Pat. No. 4,697,792 (Fink), U.S. Pat. No. 6,572,675 (Yerushalmi) and U.S. Pat. No. 6,676,888 (Mansell) over a conventional fixed rotary furnace (two opposed operational entry points), are:                Rapid pouring of the molten metal (controlled via gravity)        Rapid pouring of the molten metal residue (salts, aluminium oxides, etc) that results post processing the scrap metal.        Larger heat transfer surface area with the furnace wall which permits higher heat transfer between the furnace internal refractory walls and the metal scrap, hence accelerate the melting process, with reduced fuel usage.        Larger gases resident time—two passes for the hot combustion gases along the longitudinal path of the rotary furnace (two flights), ensure higher heat transfer, which also translates into higher melting capacity.        
An example of using sub-stoichiometric hot gases to gasify waste from a rotary furnace is listed in U.S. Pat. No. 5,553,554 (Urich) which describes using a continuously operated furnace with two opposed entry points (and not a single entry point tilting rotary furnace) to gasify the waste. In the aforementioned patent, the organic waste is fed via a hopper with ram feeding into the rotary furnace in a continuous manner. Furthermore, in this system a burner is installed in the rotating furnace with induce air to provide direct flame heating into the furnace. The system process control does not have a mechanism to predict when the organics have been fully gasified. Hence, the system operates on a fixed processing time for the waste, irrespective of the amount of organics in the waste. This naturally lead to either overcooked waste material (wasting of energy), or undercooked material (organics are not fully burned, and the waste still smothering at the exit of the furnace with the ash material (which creates both environmental issues and loss of potential energy in the form of unburned hydrocarbon). A further problem with such furnaces is that when the furnace door is opened to allow more material to be loaded into the furnace this allows oxygenated gas (air) into the furnace, resulting in a lowering of temperature and oxidisation of the metal.